1. Field of the Invention
This invention relates to the field of frequency detection circuits, and in particular to a clock frequency detector which is insensitive to power supply variations.
2. Description of the Related Art
Microprocessor frequencies are getting higher every year even as power supply voltages are being decreased to allow increased device densities and decreased power consumption. Clock circuit designs must be constantly improved to keep up. As a microprocessor proceeds through its power-up sequence, one of the very first steps is to obtain a clock signal within the specified operating parameters. A microprocessor will typically include a clock frequency detector to determine when the clock signal is within the range required for proper microprocessor operation. It is desirable for the clock frequency detector to have precise trip frequencies over a range of process variations to ensure that the provided clock frequency is within the specified range. It is also desirable that the operation of the clock frequency detector be insensitive to variations in the power supply voltage since various power supply voltages are being employed with any given microprocessor architecture to provide multiple performance vs. portability trade-off points.